freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/es6/explore-differences-between-the-var-and-let-keywords.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
587d7b87367417b2b2512b3f	Explore Differences Between the var and let Keywords	1	301202	explore-differences-between-the-var-and-let-keywords

--description--

One of the biggest problems with declaring variables with the var keyword is that you can overwrite variable declarations without an error.

var camper = 'James';
var camper = 'David';
console.log(camper);

Here the console will display the string David.

As you can see in the code above, the camper variable is originally declared as James and then overridden to be David. In a small application, you might not run into this type of problem, but when your code becomes larger, you might accidentally overwrite a variable that you did not intend to overwrite. Because this behavior does not throw an error, searching and fixing bugs becomes more difficult.
A new keyword called let was introduced in ES6 to solve this potential issue with the var keyword. If you were to replace var with let in the variable declarations of the code above, the result would be an error.

let camper = 'James';
let camper = 'David';

This error can be seen in the console of your browser. So unlike var, when using let, a variable with the same name can only be declared once. Note the "use strict". This enables Strict Mode, which catches common coding mistakes and "unsafe" actions. For instance:

"use strict";
x = 3.14;

This will display an error that x is not defined.

--instructions--

Update the code so it only uses the let keyword.

--hints--

var should not exist in the code.

(getUserInput) => assert(!getUserInput('index').match(/var/g));

catName should be the string Oliver.

assert(catName === 'Oliver');

quote should be the string Oliver says Meow!

assert(quote === 'Oliver says Meow!');

--seed--

--seed-contents--

var catName;
var quote;
function catTalk() {
  "use strict";

  catName = "Oliver";
  quote = catName + " says Meow!";

}
catTalk();

--solutions--

let catName;
let quote;
function catTalk() {
  'use strict';

  catName = 'Oliver';
  quote = catName + ' says Meow!';
}
catTalk();